Synthesis and structural investigation of N,N′,N″ -trialkylguanidinato-supported zirconium(IV) complexes

Article abstract of DOI:10.1021/ic034445a

The addition of 2 equiv of N,N′,N″-triisopropylguanidine (guanH₂) to Zr(CH₂Ph)₄ produced the bis(guanidinato)bis(benzyl)zirconium complex {(ⁱPrNH)C(N ⁱPr)₂}₂Zr(CH₂Ph)₂ (1). The mono(guanidinato) complex {(ⁱPrN)₂C(NH ⁱ-Pr)}ZrCl₃ (2) was accessible by the reaction of 2 equiv of guanH₂ with ZrCl₄. Guanidinium hydrochloride, {C(NHⁱPr)3}Cl, is a byproduct of this reaction. When crystallized from THF, complex 2 was isolated as the THF adduct {(ⁱPrNH)C(N ⁱPr)₂}ZrCl₃(THF) (2-THF). The mixed cyclopentadienyl guanidinato complex {η⁵-1,3-(Me ₃Si)₂C₅H₃}{( ⁱPrNH)C(NⁱPr)₂}ZrCl₂ (3) was prepared by treatment of {1,3-(Me₃Si)₂C₅H ₃}ZrCl₃ with the in situ generated lithium triisopropylguanidinate salt. The reaction of guanH₂ with {1,3-(Me₃Si)₂C₅H₃}ZrMe₃ affords the dimethyl derivative {η⁵-1,3-(Me₃Si) ₂C₅H₃}{(ⁱPrNH)C(N ⁱPr)₂}ZrMe₂ (4). Definitive evidence for the molecular structures of these products is provided through single-crystal X-ray characterization of 1, 2-THF, and 3, which are presented. The extent of π delocalization within the guanidinato ligand is discussed in the context of the metrical parameters obtained from these structural studies.

Full text of DOI:10.1021/ic034445a

Inorg. Chem. 2003, 42, 6225−6229
Synthesis and Structural Investigation of
N,N′,N′′-Trialkylguanidinato-Supported Zirconium(IV) Complexes
Patrick Bazinet, Dayna Wood, Glenn P. A. Yap, and Darrin S. Richeson*
Department of Chemistry, UniVersity of Ottawa, Ottawa, Ontario, Canada K1N 6N5
Received April 28, 2003
The addition of 2 equiv of N,N′,N′′-triisopropylguanidine (guanH ) to Zr(CH Ph)4 produced the bis(guanidinato)-
2
2
i
i
i
i
bis(benzyl)zirconium complex {(PrNH)C(NPr)2}2Zr(CH Ph)2 (1). The mono(guanidinato) complex {(PrN)2C(NH-
2
Pr)}ZrCl3 (2) was accessible by the reaction of 2 equiv of guanH with ZrCl4. Guanidinium hydrochloride,
2
i
{C(NHPr)3}Cl, is a byproduct of this reaction. When crystallized from THF, complex 2 was isolated as the THF
adduct {(PrNH)C(NPr)2}ZrCl3(THF) (2-THF). The mixed cyclopentadienyl guanidinato complex {η5-1,3-(Me3-
i
i
i
i
Si)2C H }{(PrNH)C(NPr)2}ZrCl2 (3) was prepared by treatment of {1,3-(Me3Si)2C H }ZrCl3 with the in situ generated
5
3
5 3
lithium triisopropylguanidinate salt. The reaction of guanH with {1,3-(Me3Si)2C H }ZrMe3 affords the dimethyl
2
5 3
i
i
derivative {η5-1,3-(Me3Si)2C H }{(PrNH)C(NPr)2}ZrMe2 (4). Definitive evidence for the molecular structures of
5
3
these products is provided through single-crystal X-ray characterization of 1, 2-THF, and 3, which are presented.
The extent of π delocalization within the guanidinato ligand is discussed in the context of the metrical parameters
obtained from these structural studies.
Introduction
NR}ZrX2] (R ) alkyl, R′ ) Me; R ) SiMe3, R′ ) aryl;
X ) halide, alkyl).5
Significant efforts to modify the reactivity of the metal-
locene framework have, over the past decade, led to the
fruitful design of new nonmetallocene complexes that
perform as single-site olefin polymerization catalysts.1
Chelating amidinate anions, [RNC(R′)NR]-, have received
attention as ancillary ligands for such applications and a
variety of cis-octahedral bis(amidinate) group 4 complexes
have been prepared.2,3 When activated with methylalumoxane
(MAO), many of these compounds have been found to be
active catalytic precursors for the polymerization of ethylene
and propylene, the oligomerization of 1,5-hexadiene, and the
isomerization of internal and terminal olefins.4 Also well
established in this regard are mono(cyclopentadienyl)-
zirconium(IV) amidinate complexes, [(η5-C5Me5){RNC(R′)-
N-substituted guanidinate anions, [RNC(NR′2)NR′′]-, have
received increasing attention as ancillary ligands for both
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R.; Kapon, M.; Botoshansky, M.; Eishen, Y.; Eisen, M. S. J. Am.
Chem. Soc. 2003, 125, 2179. (b) Averbuj, C.; Tish, E.; Eisen, M. S.
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14, 1827. (j) Flores, J. C.; Chien, J. C. W.; Rausch, M. D.
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M. S. J. Organomet. Chem. 1995, 503, 307.
(1) For selected reviews, see: (a) Gibson, V. C.; Spitzmesser, S. K. Chem.
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P. D.; Reinartz, S. Angew. Chem., Int. Ed. 2002, 41, 2236 and
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Chem. Rev. 2000, 100, 1169 and references therein.
(2) Edelmann, F. T. Top. Curr. Chem. 1996, 179, 113 and references
therein. Kilner, M.; Baker, J. Coord. Chem. ReV. 1994, 133, 219 and
references therein. Edelmann, F. T. Coord. Chem. ReV. 1994, 137,
403 and references therein.
(3) (a) Hagadorn, J. R.; Arnold, J. Organometallics 1998, 17, 1355. (b)
Hagadorn, J. R.; Arnold, J. J. Chem. Soc., Dalton Trans. 1997, 3087.
(c) Hagadorn, J. R.; Arnold, J. J. Am. Chem. Soc. 1996, 118, 893. (f)
Hagadorn, J. R.; Arnold, J. Organometallics 1994, 13, 4670.
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Keaton, R. J.; Koterwas, L. A.; Fettinger, J. C.; Sita, L. R. J. Am.
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Henningsen, D. A.; Koterwas, L. A.; Sita, L. R. J. Am. Chem. Soc.
2001, 123, 6197. (e) Jayaratne, K. C.; Sita, L. R. J. Am. Chem. Soc.
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Chem. Soc., Dalton Trans. 1996, 939. (g) Gomez, R.; Duchateau, R.;
Chernega, A. N.; Teuben, J. N.; Edelmann, F. T.; Green, M. L. H. J.
Organomet. Chem. 1995, 491, 153. (h) Gomez, R.; Duchateau, R.;
Chernega, A. N.; Meetsma, A.; Edelmann, F. T.; Teuben, J. H.; Green,
M. L. H. J. Chem. Soc., Dalton Trans. 1995, 217. (i) Gomez, R.; Green,
M. L. H.; Haggitt, J. L. J. Chem. Soc., Chem. Commun. 1994, 2607.
10.1021/ic034445a CCC: $25.00 © 2003 American Chemical Society
Published on Web 09/04/2003
Inorganic Chemistry, Vol. 42, No. 20, 2003 6225

Bazinet et al.
Schlenk techniques. ZrCl4 and MeLi (1.4 M in diethyl ether) was
used as received from Aldrich Chemical Co. Solvents were distilled
main-group and transition-metal complexes due to their
flexible coordination behavior and their potentially tunable
steric and electronic properties.6-10 Guanidinate complexes
are now beginning to emerge as interesting species in small-
molecule activation.7d,9a,b
A characteristic feature of guanidinate ligands is the
presence of the NR′2 function that is capable of donating
lone pair electron density to the central carbon of the ligand
and stabilizing a zwitterionic resonance structure (I). This
results in formal negative charges on both of the metal-
bonded nitrogen atoms and might ultimately lead to increased
electron donation to the metal.
1
from Na/K alloy under nitrogen. H and 13C NMR spectra were
run on a Varian Gemini-200, a Bruker 300 MHz, or a Bruker 500
MHz spectrometer using the residual protons of the deuterated
solvent for reference. Zr(CH2Ph)4 was prepared using literature
procedures. {η5-1,3-(Me3Si)2C5H3}ZrCl3 was prepared by the
reaction of 1,1,3-(Me3Si)3C5H3 with ZrCl4. {η5-1,3-(Me3Si)2C5H3}-
ZrMe3 was prepared by the reaction of MeLi with {η5-1,3-(Me3-
Si)2C5H3}ZrCl3.
{(iPrN)2C(NHiPr)}2Zr(CH2Ph)2 (1). To an orange solution of
Zr(CH2Ph)4 (0.173 g, 0.380 mmol) dissolved in 2 mL of dichlo-
romethane was added a colorless 2 mL dichloromethane solution
of triisopropylguanidine (0.146 g, 0.788 mmol). An immediate color
change to clear yellow was observed. The mixture was allowed to
sit at room temperature undisturbed for 72 h. The solvent was then
removed to give a light yellow solid (0.214 g, 88% yield). Yellow
crystals of 1 were obtained from diethyl ether at -35 °C.
1H NMR (C6D6): δ 0.90 (m, 12H, CH3), 1.13 (d, 24H, CH3),
2.67 (s, 4H, CH2), 3.48 (br, 4H, CH and NH), 3.64 (sept, 4H, CH),
6.92 (t, 1H, C6H5), 7.26 (t, 2H, C6H5), 7.45 (d, 2H, C6H5). 13C
NMR (C6D6): δ 24.6, 24.8 (CH3), 46.3, 46.8 (CH), 70.9 (CH2),
119.8, 127.4, 128.2, 150.7 (C6H5), 168.6 (CN3).
To maximize this effect the NR′2 center should be sp2
hybridized with the lone electron pair residing in a p-orbital
that is oriented to overlap with the conjugated NCN moiety.
This second feature requires a small dihedral angle between
the planes defined by the CNR′2 groups and that defined by
NCN chelate. It is worth noting that the attendant steric
congestion caused by the two organic substituents should
encourage a larger dihedral angle and disfavor the appropriate
orientation for π conjugation. Our efforts to encourage
resonance contribution I have, as one focus, the application
of N,N′,N′′-trialkylguanidinato ligands which possess a less
sterically demanding exocyclic N(H)R′ group.
Herein we present the synthesis and characterization of
zirconium(IV) complexes with triisopropylguanidinato- and
mixed cyclopentadienyl/guanidinato-supporting ligation. The
guanidinate anion was introduced into the coordination
sphere of Zr(IV) through proton-transfer coupled with HCl
or hydrocarbon elimination reactions and through salt me-
tathesis reactions. Metrical parameters of the guanidinato
ligands have been examined using X-ray crystallography and
are discussed in relation to resonance structure I.
Anal. Calcd for ZrN6C34H58: C, 63.60; H, 9.11; N, 13.09.
Found: C, 63.20; H, 8.96; N, 13.40.
{(iPrN)2C(NHiPr)}ZrCl3 (2). To a suspension of ZrCl4 (0.626
g, 2.686 mmol) in 30 mL of toluene was added a toluene solution
of triisopropylguanidine (0.996 g, 5.372 mmol). The mixture was
allowed to stir for 16 h. Filtration and removal of solvent gave a
fluffy white solid (0.612 g, 60% yield). The insoluble materials
were identified as guanidinium hydrochloride ((iPrNH)3CCl) by
comparison with spectroscopic parameters of an authentic sample.
1H NMR (C6D6): δ 0.83 (d, 6H, CH3), 1.45 (d, 12H, CH3), 3.52
(broad, 4H, CH and NH). 13C NMR (C6D6): δ 24.30 (CH3), 24.64
(CH3), 46.71 (CH), 47.40 (CH), 148.67 (CN3).
Anal. Calcd for ZrN3C10H22Cl3: C, 31.45; H, 5.81; N, 11.00.
Found: C, 31.25; H, 5.96; N, 10.70.
Recrystallization of 2 from THF at at -35 °C yielded crystals
of the THF adduct of 2, which were analyzed by single-crystal
X-ray analysis.
{1,3-(Me3Si)2C5H3}{(iPrN)2C(NHiPr)}ZrCl2 (3). Dropwise ad-
dition of methyllithium (0.9 mL of 1.4 M, 1.26 mmol) to a solution
of triisopropylguanidine (0.233 g, 1.26 mmol) dissolved in about
30 mL of ether produced a colorless reaction mixture that was stirred
for 40 min. Solid 1,3-(Me3Si)2CpZrCl3 (0.52 g, 1.28 mmol) was
added to this reaction mixture. The solution turned orange/red and
eventually became a pale yellow followed by formation of a
precipitate. The reaction was stirred overnight, and all volatiles were
removed under vacuum. The product was extracted in 40 mL of
hexane, which was filtered through a Celite pad, and the volatiles
were removed to yield the product as a yellow solid (0.40 g, 58%).
The product could then be further purified by recrystallization from
diethyl ether at -25 °C.
1H NMR (C6D6): δ 0.38 (s, 18H, Si(CH3)3), 0.74 (d, 6 H, CH-
(CH3)2), 1.27 (d, 12 H, CH(CH3)2), 3.38 (sept, 1H, CHMe2), 3.59
(overlapping br, 1H, NH, and sept, 2H, CHMe2), 6.98 (d, 2H, Cp
H), 7.13 (t, 1H, Cp H). 13C NMR (C6D6): δ 0.1 (Si(CH3)3), 23.4
(CH(CH3)2), 24.0 (CH(CH3)2), 45.8 (CHMe2), 48.0 (CHMe2), 125.4
(Cp H), 130.4 (Cp-Si), 131.1 (Cp H), 162.0 (CN3).
Experimental Section
General Considerations. All manipulations were carried out in
either a nitrogen-filled drybox or under nitrogen using standard
(6) Bailey, P. J.; Pace, S. Coord. Chem. ReV. 2001, 214, 91 and references
therein.
(7) (a) Foley, S. R.; Yap, G. P. A.; Richeson, D. S. Inorg. Chem. 2002,
41, 4149. (b) Ong, T.-G.; Wood, D.; Yap, G. P. A.; Richeson, D. S.
Organometallics 2002, 21, 2839. (c) Foley, S. R.; Yap, G. P. A.;
Richeson, D. S. Polyhedron 2002, 21. 619. (d) Ong, T.-G.; Wood,
D.; Yap, G. P. A.; Richeson, D. S. Organometallics 2002, 21, 1. (e)
Lu, Z.; Yap, G. P. A.; Richeson, D. S. Organometallics 2001, 20,
706. (f) Foley, S. R.; Yap, G. P. A.; Richeson, D. S. J. Chem. Soc.,
Chem. Commun. 2000, 1515. (g) Thirupathi, N.; Yap, G. P. A.;
Richeson, D. S. Organometallics 2000, 19, 2573. (h) Thirupathi, N.;
Yap, G. P. A.; Richeson, D. S. J. Chem. Soc., Chem. Commun. 1999,
2483. (i) Wood, D.; Yap, G. P. A.; Richeson, D. S. Inorg. Chem.
1999, 38, 5788.
(8) Coles, M. P.; Hitchcock, P. B. J. Chem. Soc., Dalton Trans. 2001,
1169.
(9) (a) Mullins, S. M.; Duncan, A. P.; Bergman, R. G.; Arnold, J. Inorg.
Chem. 2001, 40, 6952. (b) Duncan, A. P.; Mullins, S. M.; Arnold, J.;
Bergman, R. G. Organometallics 2001, 20, 1808. (c) Giesbrecht, G.
R.; Arnold, J. J. Chem. Soc., Dalton Trans. 2001 923. (d) Giesbrecht,
G. R.; Whitener, G. D.; Arnold, J. Organometallics 2000, 19, 2809.
(10) Okamoto, S.; Livinghouse, T. Organometallics 2000, 19, 1449.
We were unable to obtain satisfactory microanalysis for 3. As
alternative support of the purity of this compound, the 1H and 13
C
NMR spectra of 3 are included in the Supporting Information.
6226 Inorganic Chemistry, Vol. 42, No. 20, 2003

Trialkylguanidinato-Supported Zr(IV) Complexes
Table 1. Selected Crystal Data and Data Collection Parameters for {(iPrN)2C(NHiPr)}2Zr(CH2Ph)2 (1), {(iPrN)2C(NHiPr)}ZrCl3(THF) (2-THF), and
{1,3-(Me3Si)2C5H3}{(iPrN)2C(NHiPr)}ZrCl2 (3)
empirical formula
fw
C34H58N6Zr (1)
642.08
C14H30Cl3N3OZr (2-THF)
453.98
C21H43Cl2N3Si2Zr (3)
555.88
T (K)
203(2)
203(2)
203(2)
wavelength (Å)
cryst system
space group
a (Å)
b (Å)
c (Å)
0.710 73 (Mo KR)
monoclinic
P21/n
10.4142(13)
15.2097(19)
22.600(3)
96.563(2)
3556.3(8)
4
0.710 73 (Mo KR)
monoclinic
Cc
0.710 73 (Mo KR)
orthorhombic
Pbca
14.706(1)
19.030(2)
9.424(2)
15.105(4)
15.152(4)
104.70(2)
2086(2)
20.916(2)
â (deg)
V (Å3)
5853(1)
8
0.652
R1 ) 0.0507
wR2 ) 0.1394
Z
4
abs coeff (mm-1
)
0.339
R1 ) 0.0325
wR2 ) 0.0639
0.915
R1 ) 0.0586
wR2 ) 0.1665
final R indices [I > 2σ(I)]a
2
a R1 ) Σ|Fï| - |Fc|/Σ|Fï|. wR2 ) (Σw(|Fo| - |Fc|)2/Σw|Fo| )1/2
.
CHMe2), 6.72 (d, 2H, Cp H), 6.99 (t, 1H, Cp H). 13C NMR
(C6D6): δ 0.36 (Si(CH3)3), 24.1 (CH(CH3)2), 24.5 (CH(CH3)2), 40.7
(Zr-CH3), 46.1 (CHMe2), 47.1 (CHMe2), 121.2 (Cp H), 124.9
(Cp-Si), 127.6 (Cp H), 167.3 (CN3).
We were unable to obtain satisfactory microanalysis for 4. As
alternative support of the purity of this compound, the 1H and 13
C
NMR spectra of 4 are included in the Supporting Information.
Results and Discussion
The direct reaction of a 1:2 molar ratio of Zr(CH2Ph)4
and N,N′,N′′-triisopropylguanidine, (iPrN)dC(NHiPr)2, in
toluene at room temperature proceeds via proton transfer and
toluene elimination to yield a new species [{(iPrNH)C(Ni-
Pr)2}2Zr(CH2Ph)2] (1) in 88% isolated yield (eq 1).7d The
1H and 13C NMR spectra of 1 display two sets of iPr signals
in a 2:1 ratio and a single methylene resonance attributed to
the benzyl ligands. Complex 1 is stable for at least 24 h at
temperatures up to 100 °C even in the presence of excess
N,N′,N′′-triisopropylguanidine. To establish the molecular
structure of 1 a single-crystal X-ray analysis was undertaken
and the results are presented in Figure 1 and Tables 1 and
2. Complex 1 exhibits two guanidinato ligands that span
axial/equatorial positions. The N(1)-Zr-N(4) angle of
155.96(5)° supports the assignment of N(1) and N(4) to the
pseudoaxial positions of a distorted octahedral complex with
approximate C2 symmetry. The equatorial plane is defined
by two guanidinato nitrogens (N(2) and N(5)) and the two
benzyl groups. Structural analysis confirmed the lack of η2
bonding for the benzyl groups.
Figure 1. Molecular structure and atom numbering scheme for {(iPrN)2C-
(NHiPr)}2Zr(CH2Ph)2 (1).
Table 2. Selected Bond Distances and Angles for
{(iPrN)2C(NHiPr)}2Zr(CH2Ph)2 (1)
Bond Distances (Å)
Zr-N(1)
2.290(2)
2.295(2)
2.312(2)
1.327(2)
1.348(2)
1.378(2)
Zr-N(2)
2.209(2)
2.188(2)
2.312(2)
1.335(2)
1.345(2)
1.370(2)
Zr-N(4)
Zr-N(5)
Zr-C(28)
N(1)-C(10)
N(2)-C(10)
N(3)-C(10)
Zr-C(21)
N(4)-C(20)
N(5)-C(20)
N(6)-C(20)
Bond Angles (deg)
N(4)-Zr-N(2)
101.96(6) N(1)-C(10)-N(3)
59.27(5) N(2)-C(10)-N(3)
59.40(6) N(5)-C(20)-N(4)
105.94(6 ) N(5)-C(20)-N(6)
93.02(7) N(4)-C(20)-N(6)
125.3(2)
N(2)-Zr-N(1)
122.1(2)
112.1(2)
123.7(2)
124.7(2)
111.5(1)
112.7(1)
N(4)-Zr-N(5)
N(1)-Zr-N(5)
C(28)-Zr-C(21)
C(10)-N(3)-C(7)
C(20)-N(6)-C(17)
N(1)-C(10)-N(2)
N(1)-N(2)-C(10)/
C(9)-C(10)-N(3)a
122.6(2)
123.5(2)
112.6(2)
56.2
C(27)-C(21)-Zr
C(34)-C(28 )-Zr
N(4)-N(5)-C(20)/
C(19)-C(20)-N(6)a
52.2
a The angle between the planes of the chelate (N-C-N) and the
isopropylamino substituent.
{1,3-(Me3Si)2C5H3}{(iPrN)2C(NHiPr)}ZrMe2 (4). A toluene
solution of triisopropylguanidine (0.185 g, 1 mmol) was added to
1,3-(Me3Si)2CpZrMe3 (0.345 g, 1 mmol) dissolved in about 20 mL
of toluene. The reaction was allowed to stir at room-temperature
overnight. All volatiles were removed under vacuum to leave a
white solid that was identified as pure 4 (0.510 g, 99%).
1H NMR (C6D6): δ 0.31 (s, 18H, Si(CH3)3), 0.44 (s, 6H, ZrCH3)
0.88 (d, 6 H, CH(CH3)2), 1.18 (d, 12 H, CH(CH3)2), 3.48
(overlapping br, 1H, NH, and sept, 2H, CHMe2), 3.58 (sept, 1H,
The spectroscopic equivalence for the iPr groups (both CH
and CH3) bonded to N(1) and N(4) with those on N(2) and
N(5) as well as the appearance of a singlet for the benzylic
protons indicates that the guanidinato ligands in 1 are
fluxional in solution. Furthermore, this exchange occurs only
Inorganic Chemistry, Vol. 42, No. 20, 2003 6227

Bazinet et al.
Table 3. Selected Bond Distances and Angles for
{(iPrN)2C(NHiPr)}ZrCl3(THF) (2-THF)
Bond Distances (Å)
Zr-N(1)
2.13(2)
2.27(2)
1.34(2)
1.34(3)
1.35(3)
Zr-N(2)
Zr-Cl(1)
Zr-Cl(2)
Zr-Cl(3)
2.15(2)
Zr-O(1)
2.450(9)
2.439(7)
2.412(7)
N(1)-C(10)
N(2)-C(10)
N(3)-C(10)
Bond Angles (deg)
N(1)-Zr-N(2)
61.8(6) C(10)-N(2)-C(4)
174.5(5) C(10)-N(2)-Zr
154.9(5) C(4)-N(2)-Zr
159.0(5) C(10)-N(3)-C(7)
123(2)
93.8(1) N(1)-C(10)N(2)
140.0(2) N(3)C(10)-N(2)
30.3
123.7(2)
O(1)-Zr-Cl(3)
N(2)-Zr-Cl(2)
N(1)-Zr-Cl(1)
C(10)-N(1)-C(1)
C(10)-N(1)-Zr
C(1)-N(1)-Zr
92.8(1)
142.3(2)
129.8(2)
N(1)-C(10)-N(3) 127.8(2)
111.1(2)
121.1(2)
Figure 2. Molecular structure and atom numbering scheme for {(iPrN)2C-
(NHiPr)}ZrCl3(THF) (2-THF).
C(7)-N(3)-C(10)/
N(1)-C(10)-N(2)a
a The angle between the planes of the chelate (N-C-N) and the
isopropylamino substituent.
between the nitrogen centers bonded to Zr and does not
involve the noncoordinated NH(iPr) groups of the guanidinato
ligands. These observations are similar to those for the
recently reported complex [{(Me2N)C(NiPr)2}2Zr(CH2Ph) 2]
(A).9b
The bond distances around N(1), N(2), and C(10) and
N(4), N(5), and C(20) average 1.34 Å indicating partial
double-bonding character and a π-conjugated NCN chelate.
The N(3)-C(10) and N(6)-C(20) bond distances of 1.378(2)
and 1.370(2) Å are shorter than a typical C-N single bond
of 1.42-1.45 Å and also shorter than the Me2N-C distance
in A of 1.394(4) and 1.385(4) Å.9b The only measurable
angles about N(3) (122.33(15)°) and N(6) (123.25(16)°) are
consistent with sp2-hybridized nitrogen atoms. However, the
dihedral angles between the N(H)iPr groups and the N-C-N
chelate rings (average 54°) indicate little contribution from
resonance structure I.
Guanidinato ligands can also be introduced into the Zr
coordination sphere by the reaction shown in eq 2. This
method employs 2 equiv of neutral guanidine in reaction with
zirconium tetrachloride. We anticipated that 1 equiv of
guanidine would be incorporated into a new complex, 2, with
the second 1 equiv facilitating the removal of HCl and
forming guanidinium hydrochloride. When the reaction of
N,N′,N′′-tri(isopropyl)guanidine with ZrCl4 was carried out
in toluene the two products could be easily separated on the
basis of differing solubility. The NMR spectra of 2 indicate
the presence of the guanidinato ligand with a characteristic
ratio of 2:1 isopropyl groups.
Figure 3. Molecular structure and atom numbering scheme for {1,3-(Me3-
Si)2C5H3}{(iPrN)2C(NHiPr)}ZrCl2 (3).
three chlorides in support of the formulation of 2. In addition,
2-THF has one molecule of THF that completes the
coordination sphere of the Zr(IV) center.
The equivalent N(2)-C(10) and N(1)-C(10) bond dis-
tances (1.34(2) Å) are consistent with partial double-bond
character and support π delocalization over an sp2-hybridized
core. The fact that the N(3)-C(10) bond distance is
equivalent to those in the chelate ring (1.35(2) Å) and that
the angle between the C(7)-N(3)-C(10) plane and the plane
defined by N(1)-C(10)-N(2) is only 30.3° indicates that,
in contrast to complex 1, the zwitterionic resonance structure
for the guanidato ligand is important in this complex. Further
support for the contribution of I is given by the observation
that the average Zr-N bonds in 2-THF are 0.11 Å shorter
than the average Zr-N distances of 1. Although these effects
are subtle, these data suggest that the electronic environment
at the metal center has some bearing on the extent of π
donation from the exocyclic iPrNH group and, hence, to the
overall donor strength of the guanidinato ligand. The ligand
appears to act as a more powerful electron donor toward the
relatively electron poor metal center of complex 2-THF
compared to more electron-rich metal center of 1.
ZrCl4 + 2(iPrNH)2C(NiPr) f
+ (iPrNH) CCl (2)
i
i
Cl3Zr{( PrN)2C(NH Pr)}
3
2
Complexes with a combination of guanidinato- and cy-
clopentadienyl-supporting ligands are directly related to
mono(cyclopentadienyl)zirconium(IV) amidinato.5 We have
explored two routes to such complexes that are summarized
in eq 3. The reaction of the appropriate monocyclopentadi-
enyl zirconium starting materials with lithium guanidinate
or guanidine offer two methods for preparation of complexes
with mixed supporting ligands. The lithium salt of N,N′,N′′-
Although we have been unable to obtain crystals of 2 that
were satisfactory for single-crystal structural analysis, re-
crystallization from THF did yield single crystals (2-THF)
that were subjected to X-ray diffraction analysis. The results
of this study are summarized in Tables 1 and 3 and displayed
in Figure 2. Complex 2-THF possesses a distorted octahedral
geometry with a single cis-chelating guanidinato ligand and
6228 Inorganic Chemistry, Vol. 42, No. 20, 2003

Trialkylguanidinato-Supported Zr(IV) Complexes
Table 4. Selected Bond Distances and Angles for
{1,3-(Me3Si)2C5H3}{(iPrN)2C(NHiPr)}ZrCl2 (3)
C(10)-N(3) bond length of the guanidinato ligand in 3 of
1.358(6) Å is equivalent to the C-N distances within the
chelate ring (1.355(6), 1.347(5) Å) suggesting a significant
degree of double-bond character between these atoms. This
is likely the result lone pair π donation from the N(H)iPr
group to the central carbon of the chelate ring and suggests
that resonance structure I is significant for 3. Consistent with
this proposal are the small angle between the two planes
defined by C7-N3-C10 and N1-C10-N2 of 30.3° and
the Zr-N bond lengths that are between those of 1 and 2. A
comparison of these metrical parameters with the recently
reported of tetrasubstituted guanidinate-bearing complex
CpZr((iPrN)2CNMe2)Cl2 (B)9b suggests that replacing the
exocyclic NMe2 group with a less sterically demanding
N(iPr)H favors resonance contribution I. Specifically, B
displayed a larger dihedral angle (44.78°) between the Me2N
plane and the CNC plane of the chelate ring and a longer
C-NMe2 bond length (1.373(4) Å) than did 3.
Bond Distances (Å)
Zr-Cl(1)
2.435(1)
2.194(3)
1.355(6)
1.347(5)
2.533(4)
2.530(4)
Zr-Cl(2)
2.491(1)
2.214(4)
1.358(6)
2.550(4)
2.560(4)
2.567(4)
Zr-N(1)
Zr-N(2)
N(1)-C(10)
N(2)-C(10)
Zr-C(13)
Zr-C(15)
N(3)-C(1)
Zr-C(12)
Zr-C(14)
Zr-C(11)
Bond Angles (deg)
C(1)-Zr-Cl(2)
91.36(3)
111.1(3)
30.1
N(1)-Zr-N(2)
C(9)-N(3)-C(1)
60.43(9)
121.0(3)
N(1)-C(1)-N(2)
N(1)-C(10)-N(2)/
C(10)-N(3)-C(7)a
a The angle between the planes of the chelate (N-C-N) and the
isopropylamino substituent.
trisisopropylguanidinate was generated by in situ deproto-
nation of guanidine with MeLi. Reaction with 1,3-
(Me3Si)2CpZrCl3 proceeds smoothly to generate 3 with
elimination of LiCl. The mono(cyclopentadienyl)(guanidi-
nato)zirconium dimethyl analogue can be prepared by the
direct reaction of 1,3-(Me3Si)2CpZrMe3 and N,N′,N′′-triiso-
propylguanidine. In this case the guanidinate is deprotonated
by one of the zirconium methyl groups with elimination of
methane to yield 4.
Conclusions
We have shown that neutral organozirconium complexes
bearing guanidinato ancillary ligands can be synthesized and
isolated by employing alkane, HCl, and LiCl elimination
reactions. Structural investigations indicate that π donation
from the isopropylamino moiety of the guanidinato ligand
plays a role in some of these complexes. We are currently
investigating the implications of this electronic effect on the
reactivity of guanidinato-supported complexes. Along with
this effort, our continuing investigations are oriented at
further revealing the steric and electronic features that
influence the reactivity of transition metal guanidinate
compounds.
Acknowledgment. This work was supported by the
NSERC of Canada. P.B. is the recipient of an NSERC
Postgraduate Scholarship.
The NMR spectra of complexes 3 and 4 are similar and
clearly support the formulations of eq 3. To confirm the
structural details for these species and to examine the metrical
parameters for the guanidinato ligand the molecular structure
of 3 was determined by single-crystal X-ray diffractometry.
The results of this analysis are summarized in Table 1 and
depicted in Figure 3. Selected bond lengths and angles are
provided in Table 4.
Supporting Information Available: Crystallographic data in
CIF format and tables of crystal data and structure solution and
refinement details, atomic coordinates, bond lengths and angles,
and anisoptropic thermal parameters for compounds 1, 2-THF, and
3 and 1H and 13C NMR spectra of 3 and 4. This material is available
free of charge via the Internet at http://pubs.acs.org.
The structural parameters for the guanidinato ligand in 3
are similar to those observed for 2-THF. Specifically, the
IC034445A
Inorganic Chemistry, Vol. 42, No. 20, 2003 6229